Mount alternator on top of back tire?

george_n_texas

george_n_texas

Member
Whadyathink??? If you made a jig like they test alternators in the parts store on top of where a bike rack goes will it charge your batteries to run lights and extend the distance of your hub mount motor? The exact setup I am concocting (In my head) is 3 deep cell batteries and about a 2 gallon tank mounted on a trailer to end up with a hybrid bike. Alternators with a serpentine belt drive have pulleys about the same width as a bike tire. This would be much the same setup as the roller drive engines utilize now. I figure a mile has 5280 feet and a bike goes roughly 25 MPH so that's 25 X 5280 = 13200 feet per hour
13200 feet / 60 minutes = 2200 feet per minute
I am assuming most pullies are < 1' in circumference which means 2200 RPM

If I get 100 MPG and I bought quality deep cell batteries I would venture to say between 3-400 mile range might be possible.

I have seen claims of a penny a mile on electric consumption anyone have real figure on that?

Gas even at $4 a gallon equals to about 4 cents a mile at 100 MPG.

kidcrash, Addicted To Bikes and me were playing with this idea in the chat lounge...was fun guys!.trlrl.
 
The added drag would reduce the efficiency of the setup - to what extent I'm not sure. While yer not proposing the fabled "perpetual motion" machine, your numbers may not be as beneficial as they seem on paper.

However - having a true hybrid, both gas AND electric and using the gas motor to help recharge the electric is an awesome idea! Instead of an alternator set up as friction-driven... I wonder about the belt drive rim set-up the Wizzers use?

I built one with a 33cc 2stroke friction drive and a 'Zap' electric drive, the Zap would act as a (somewhat weak) generator when it was engaged but not powered. As I didn't use the electric much unless I was downtown - the batteries always remained topped off and ready to use. I have no idea if the hub motors generate when spun, some motors do - some don't... It's sometimes referred to as "regenerative braking" with electric vehicles. I don't remember the difference... brushed/brushless mebbe? *shrug* ahh... I forget lol

The only problems I had with that setup was the usual woes of rack mount friction drives. Although - if you were to pursue your idea, I'd recommend a much smaller unit than your standard automotive alternator. There are tiny lil ones sometimes found on motorcycles (I believe the Honda Goldwing may be one), even some of the friction generators found for bike lighting are 12v and would help trickle charge during daytime use. Of course you would need a regulator if you weren't using an alternator - which usually have them built in.

Despite many stories to the contrary, it's actually quite difficult to spin an alternator fast enough to generate a charge. The "I wanna make a wind generator" is a common example of the problems involved with drag/RPM. If yer determined, there are many small DC engines that work quite well as generators and are smaller/lighter... but I haven't looked into those myself. ;)


Don't mind me... I'm jus babbling a bit and musing lol
 
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Hi George - The idea of using forward motion to turn any type of generating device needs to be tempered by the realization that the amount of power used (or generated) will come off the top of your power source (as drag, as BarelyAwake noted) It won't matter whether you turn the generator/alternator by the wheel or directly from the power source. If you're drawing a little current, like to run efficient LED lights, it won't create much drag. But if you are trying to charge 36 volts of discharged deep cycle 20ah SLA in a short time, the drag will be enormous. The concept of "regenerative braking" demonstrates this - a Prius can be stopped in a short distance just using regen. The power gets dumped into the batteries, but it is effectively drag on the wheels and that's what slows it so quickly. "They" say 750 watts is one hp so for every 750 watts you are generating, yer little China girl is going to have 1 less hp to push you along. Lack of efficiency will push that in the wrong direction even farther. If you were pedaling, it would feel like one of those slow-motion bad dreams.

As long as you are going with gas you should probably go with the minimal amount of generator and battery that you would need, and it might be best if the electric motor you use could double as your generator. Just a few thoughts - jd
 
George,
I've thought about close to the same rig, but just to charge my lighting battery for my china bike. haven't found one that was small enough, self contained, and CHEAP enough on my meegger paycheck!
 
George, you have to consider the fact that a car alternator works great in a car because it has a powerful gasoline engine turning it at thousands of RPMs and it's mainly keeping the battery charged to run the car's accessories and to occasionally turn the starter for a couple of seconds. An alternator has to be turning at X number of RPMs and requires a certain amount of amps before it can even start charging. It's not likely your bike could even achieve that minimum RPMs. As jcdburg said, the drag would be enormous. You wouldn't gain anything and would lose a lot. Plus, you'd be chugging around that heavy trailer? People are dreaming up these schemes continuously and some even propose the usual propeller on the handlebars and all that kind of stuff. The bottom line is, none of this stuff is remotely close to being worth the trouble on a bike and the only hope there is for ebikes is the miracle, 5 minute charging, 100+ mile range batteries that are always "just around the corner". The primitive SLA battery will just have to do till then or just use a gas engine. That Staton setup is nifty, but you're still better off and much more efficient overall by just using a gas engine as the bike's power source in the first place. Hybrid cars and hybrid bikes are two different animals but I realize a lot of people just want to be able to say they have a hybrid bike even though it's the epitomy of innefficency.
 
o.O

starrunner - while it's true a car's alternator may be too much for a project like this, hybrid (tribrid lol) bikes like what is proposed here aren't unheard of - or even " the epitome of inefficiency". Even I have built one.

They may be a touch on the heavy side, but if you read my first post in this thread or even dig around on this forum you'll find variants on the theme that are rideable and valid. The only other major setback for these is price.

george n texas wasn't proposing the tiresome perpetual motion scheme, and while it was armchair engineering and the math may be off - the concept has potential, if perhaps with different components.

Without people pursuing what others naysay - none of us would have motorized bikes of any type.
 
I talked to an engineer at work about something like this and he shot it down because of the drag on the motor and that using an alternator would make it a perpetual motion machine of sorts. Plus you gotta consider the amount of RPMS that the alternator spins at just to put out the volts and amps to run a car. Would a 26" bicycle wheel do the same even if you are expecting less output?
 
*sigh*

Yes - perpetual motion is a waste of time to consider, yes a car alternator is too big/excessive drag, yes the RPMs are out of reasonable range.

No - all the ideas presented here aren't unreasonable, please (re)read the previous posts.
 
I still don't know what's not gonna work about this whole idea. Here's the thing I KNOW from being a trucker...when you are fully loaded 80K pounds if you can let the darn thing fly downhill staying off the brakes you get very close to the same fuel miliage as when empty...a lot of the drag comes from wind resistance and stopping an starting. The main advantage to my design is to give you more torq for starting and stopping as well as the ability to stealthily go thru towns unfriendly to gas engines on these things. I don't care if the contraption weighs 1000 pounds you could even compensate for that in electric trailer brakes and placing the electric motor as well as about as large a fuel tank and pump on the push trailer. In addition to the advantage of being able to start without peddling you also have the advantage of a power unit that could hook up to most any bike in a flash. (ever see anyone run outa gas?)

I understand one fact I did not know before which is relevant, the fact that the magnetic effects of an alternator creating amperage and voltage creates drag much as two like poles of a magnet repel against one another. Here's some fodder for you cows to chew on...the bullet train rides on top of such a field, harness that and you will have done something for sure!
Not a bird or plane, just Shanghai's new Maglev, the world's fastest train

"it's the epitomy of innefficency." starrunner

Don't hate me cause I'm beautiful LOL
 
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Hi George - Of course you CAN try whatever you want. But you asked us "Whadyathink???" I think it's not going to be very efficient either, but that is not really a priority for you. One thing I would suggest is that you think about doing this on a trike or quad. I think you're going to have serious balance and braking issues with all the weight you are talking about. Then you could sit down low in a comfortable seat and carry lots of weight too (groceries, etc) There are lots of trikes and quads out there (both pedal and powered) for you to look at. Let us know how it all comes out. jd
 
We pretty much all know most states allow 48cc and about 2hp gas engines and they also allow certain size electric motors as well. The other restriction we face generally is 20 or 30 MPH...that being said the thing I think most would like to improve on is torq to start and pull steep hills...be nice if one could use magnetic resistance to generate power going down a hill rather than hitting the brakes much as a jake brake (engine brake) works. I doubt very many if any here are riding a bike to get that 100-150 MPG it is more icing on the cake. I would think most here would be happy to get 80 MPG if it meant little to no peddling. I want to go hybrid for other reasons as well...be nice to have an inverter to run my laptop anywhere I go for one. I have AT&T broadband aircard so I could pull over at a picnic table and surf away. You wouldn't have to have big car batteries you could use motorcycle batteries such as Amazon.com: PowerStar PM12-7L Motorcycle Battery: Automotive
these weigh 6 pounds shipping so that would be 18 pounds total battery weight. someone suggested a motorcycle alternator but the post I made on hybrid with a link shows a fully dual power motor and generator in 1 unit still in developement. I gotta wonder why someone would develope something like this with no potential. I guess they could be catering to dreamers like me. I guess I could just be trippin and not dreamin LOL I don't mind being wrong I've been wrong many times before just as long as nobody is investing too much time or money I figure there's not much harm.
 
If you ran a second (as in ,harbor freight Greayhound motor/to alternator)motor t power the alt.,???
 
There is no disputing any time you convert one energy to another you loose efficientcy.

If you can capture energy like water flowing thru a dam and IMHO wheels that are spinning anyway seems to me you would benefit.

I keep hearing about the amount of friction that has to be overcome by an alternator at high output...the only time there would be a high output is when you are using the stored up energy you hopefully built up it the 100 miles you just ran on gas and for a short time if you ran the batteries way down.

I am not proposing to take fire from the magneto I am talking about an alternator's pulley resting on top of your tire.

Someone said maybe my math was off here's my formula for approximate rpm: 1 mile = 5280 feet I am assuming an alternator pulley is less than 1 foot in circumference. Your tires be they trailer 10 inch or bike 26 inch still cover the same distance.

Surely the friction of my 245 pounds on the tires grabbing at the pavement makes that alternator pale in comparison.
Have ya ever seen how hard the guy pulls down to test a load on an alternator at the auto parts store?

So if my numbers are correct 5280 feet times let's say average 20 MPH equals 105600 feet of distance divided by 60 minutes in an hour equals 1760 feet per minute hence 1760 RPM which is enough to produce nominal amps and volts from the alternator.

What would be great is if you could put a controller that would increase the amps load output from the alternator to increase if you went over say 25 MPH as you would be surely coasting downhill and restrict the load output to zero when engine rpm is low.

Here's someone who kicked this idea around in a race car...he had a switch to turn off connection to alternator during 1/4 mile race:

Switching off alternator during hard acceleration Text - Physics Forums Library

I was really just doing the armchair engineering thing but I think I'm gonna try this some day when I have more funds...unemployed and obviously boored at the time now.
 
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Hi George – What some of us referred to in earlier posts as frictional losses are really the magnetic drag you mentioned in a previous post. There are friction losses of course but they pale in comparison to the magnetic drag the generating device (alternator) would cause. As long as you realize you need the gas motor (or pedaling) to get you up to the top of the hill or to coasting speed or to turn your alternator, you will be fine. My question now is – why bother with the alternator at all? A brushed motor will act as a generator if it is being spun and isn’t drawing power. There are controllers made that have a regen circuit so they can redirect that power into the battery. In a regular car, that’s what the voltage regulator does automatically – it senses the voltage in the battery and charges it if necessary. In a hybrid car, regen can be used to slow the car. The magnetic drag can be that strong. You will already have an electric motor attached to the bike, so why add the extra weight and complexity of an alternator? Just use the motor that will already be turning and available for generating electricity to keep your battery pack charged. If you have an adjustable regen circuit you have electric brakes as well.

There are a few things you can think about that might help you plan things. 750 watts equals about 1 hp. Volts times amps equals watts, but you can turn that around into watts divided by volts equals amps. A 750 watt motor at 36 volts will draw just below 21 amps at its rated wattage. I’m pretty sure a 20 ah (amp-hour) battery pack would run that for just under an hour. There are meters you can put on your bike (Watts Up, Cycle Analyst) that can tell you how much power you are using. I don’t have one but I have run my 350 watt ebike on a 24 volt 12 ah battery pack for 15 miles/90 minutes pedal-assisting all the way and had battery left. 350/24=14.6 amps, so obviously I wasn’t drawing full power. You should probably think about how fast and far you want to go on battery so you can figure how much epower you need. Then you can figure the motor and battery size. The weight of the rig will also figure into that.

Also, you could be thinking about a way to disconnect the gas engine from the driveline when you are on electric power. A freewheel sprocket will do that, but then you will have to figure a way to start the engine. Electric start would work but will add weight. A manual clutch would let you jump-start it but I don’t know if they make them. You could use belt drive with an idler pulley. Friction drive would seem to be perfect for that. Drop it down while you’re moving to start the engine and run on gas. Lift it up for electric. Also you could pull the hinge pin, disconnect the throttle and pull the whole unit off, leaving just the electric if you wanted. A brushed hub motor probably spins easily when not generating but would act as a brake when regen is activated, so that’s what I’d think about for electric power. I’d probably want both gas and electric powering the rear to avoid any possibility of an end-over or “fork-torque” issues. As I suggested before, I’d seriously consider a trike or quad. For stability, if I was thinking trike I’d go with 2 wheels up front and front steering. More complicated but much safer IMO. Rear drive would work but then you have the motor right behind the driver’s head, depending on how low the driver sits. Lots to think about… - jd
 
I think this is a great idea and look forward to see you get it done. I am 'estupid with math so I have to build some thing to find out what I don't know, I don't know. Ya know? lol

Just thinking and typing out loud here, but instead of st8 up friction, how about a MB sprocket/ rag joint on the front wheel and mounting the alt above? Easy mount options.

I can't find it, but have a thread (or mabie just a post) rack mount some thing like this, Building your own generator. then use a standard ebike kit
 
The reason why they changed over from GENERATORS to ALTERNATORS in the old days,is because alternators will charge at LOW rpms. ATTN;This is common knowledge.A car engine that is idling is NOT high r.p.m. If your alternator in your car is not charging while the engine is idling,then IT IS BROKEN!! the FAULTY DIODE inside the alt.must be removed and replaced with a new one.If the voltage regulator is faulty,then your battery goes dead, and your car does not start.
 
If the system could be set up to run only while your going downhill or even with a wind, possibly it would be feasable.
 
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